Wet etching of samarium selenium for piezoelectric processing

ABSTRACT

A subtractive forming method that includes providing a material stack including a samarium and selenium containing layer and an aluminum containing layer in direct contact with the samarium and selenium containing layer. The samarium component of the samarium and selenium containing layer of the exposed portion of the material stack is etched with an etch chemistry comprising citric acid and hydrogen peroxide that is selective to the aluminum containing layer. The hydrogen peroxide reacts with the aluminum containing layer to provide an oxide etch protectant surface on the aluminum containing layer, and the citric acid etches samarium selectively to the oxide etch protectant surface. Thereafter, a remaining selenium component of is removed by elevating a temperature of the selenium component.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with Government support under Contract No.H98230-13-0122 awarded by Defense Advanced Research Projects Agency(DARPA). The Government has certain rights in this invention.

BACKGROUND Technical Field

The present disclosure relates generally to microelectronic fabrication,and more particularly to methods of etching samarium and seleniumcontaining layers without removing aluminum containing layers.

Description of the Related Art

With the continuing trend towards miniaturization of integrated circuits(ICs), there is a need for transistors to have higher drive currentswith increasingly smaller dimensions. Part of processing advancements toprovide smaller dimensions in microelectronic devices includeadvancements in etches processing.

SUMMARY

In one embodiment, a subtractive forming method is described herein thatincludes providing a material stack including a samarium and seleniumcontaining layer and an aluminum containing layer in direct contact withthe samarium and selenium containing layer; and masking the materialstack to expose a portion of the material stack to be etched. The methodmay continue with patterning the aluminum containing layer; and etchingthe samarium component of the samarium and selenium containing layer ofthe exposed portion of the material stack with an etch chemistrycomprising citric acid and hydrogen peroxide that is selective to thealuminum containing layer. In some embodiments, the hydrogen peroxidereacts with the aluminum containing layer to provide an oxide etchprotectant surface on the aluminum containing layer, and the citric acidetches samarium selectively to the oxide etch protectant surface. Insome embodiment, the method may continue with removing a remainingselenium component of the samarium and selenium containing layer in theexposed portion of the material stack by elevating a temperature of theselenium component above a heat of vaporization for the seleniumcomponent.

In another embodiment, a subtractive forming method is described hereinfor forming piezoresistive material stacks. The method may includeforming a mask on a first portion of the piezoresistive material stack,wherein a second portion of the piezoresistive material stack isexposed; and applying an etch chemistry to the exposed portion ofpiezoresistive material stack. The etch chemistry may include a hydrogenperoxide component for forming a surface oxide on a metal component ofthe piezoresistive material stack and a citric acid component forremoving a first element of a piezoelectric layer of the piezoresistivematerial stack selectively to the surface oxide, wherein at least onesecond element of the piezoelectric layer remains. The method mayfurther include heating the piezoelectric material stack after applyingthe etch chemistry. The heating is conducted to vaporize the at leastone second element of the piezoelectric layer that remains in saidexposed portion of said material stack, the first portion of thematerial stack being protected from being removed by said etch chemistryand said heating by said mask.

In yet another embodiment, a method of forming a device including apiezoelectric material layer is described herein. The method can includeproviding a material stack including a dielectric layer separating afirst portion of a lower electrode from a first portion of a samariumand selenium containing piezoelectric layer. A second portion of thelower electrode is in contact with a first portion of the samarium andselenium containing piezoelectric layer. The material stack furtherincludes an upper electrode layer in direct contact with a surface thesamarium and selenium piezoelectric layer that are opposite the surfaceof the samarium and selenium piezoelectric layer that is in contact withthe dielectric layer. The method may further include masking thematerial stack to expose a portion of the material stack to be etched,patterning the upper electrode layer; and etching the samarium componentof the samarium and selenium containing layer of the exposed portion ofthe material stack with an etch chemistry comprising citric acid andhydrogen peroxide that is selective to the upper electrode layer. Insome embodiments, the hydrogen peroxide reacts with the upper electrodelayer to provide an etch protectant surface on the upper electrodelayer, and the citric acid etches samarium selectively to the etchprotectant surface leaving a residue of selenium on the dielectriclayer. In a following process step, the selenium residue is removed byelevating a temperature of the selenium component above a heat ofvaporization for the selenium component.

BRIEF DESCRIPTION OF DRAWINGS

The disclosure will provide details in the following description ofpreferred embodiments with reference to the following figures wherein:

FIG. 1 is a flow chart illustrating one embodiment of a subtractiveforming method that includes an etch step for etching samarium andselenium containing layers without removing aluminum containing layers,in accordance with one embodiment of the present disclosure.

FIG. 2 is a side cross-sectional view illustrating one embodiment of apartial material stack for forming a device including a piezoelectricmaterial layer composed of a samarium and selenium containing layer, inaccordance with one embodiment of the present disclosure.

FIG. 3 is a side cross-sectional view depicting patterning a dielectriclayer of the partial material stack for forming the device including thepiezoelectric material layer to expose a portion of an electricallyconductive material layer that provides an electrode of the device, andforming a stack of a piezoelectric material layer of samarium andselenium and an aluminum containing layer, in accordance with oneembodiment of the present disclosure.

FIG. 4 is a side cross-sectional view depicting patterning the aluminumcontaining layer, in accordance with one embodiment of the presentdisclosure.

FIG. 5 is a side cross-sectional view depicting etching the samariumcomponent of the samarium and selenium containing layer of the exposedportion of the material stack with an etch chemistry comprising citricacid and hydrogen peroxide that is selective to the aluminum containinglayer followed by a high temperature process, in accordance with oneembodiment of the present disclosure.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Detailed embodiments of the claimed structures and methods are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely illustrative of the claimed structures and methods that maybe embodied in various forms. In addition, each of the examples given inconnection with the various embodiments are intended to be illustrative,and not restrictive. Further, the figures are not necessarily to scale,some features may be exaggerated to show details of particularcomponents. Therefore, specific structural and functional detailsdisclosed herein are not to be interpreted as limiting, but merely as arepresentative basis for teaching one skilled in the art to variouslyemploy the methods and structures of the present disclosure. Forpurposes of the description hereinafter, the terms “upper”, “lower”,“right”, “left”, “vertical”, “horizontal”, “top”, “bottom”, andderivatives thereof shall relate to the embodiments of the disclosure,as it is oriented in the drawing figures. The term “positioned on” meansthat a first element, such as a first structure, is present on a secondelement, such as a second structure, wherein intervening elements, suchas an interface structure, e.g. interface layer, may be present betweenthe first element and the second element. The term “direct contact”means that a first element, such as a first structure, and a secondelement, such as a second structure, are connected without anyintermediary conducting, insulating or semiconductor layers at theinterface of the two elements.

In some embodiments, the methods and structures disclosed herein providea selective etch process suitable for microelectronics fabrication, andmore particularly to selectively etching samarium and seleniumcontaining layers without removing aluminum containing layers. Thickfilm piezoelectric materials have been in industrial use for many years,but thin film piezoelectrics are relatively new. A piezoelectric (PE)material either expands or contracts, depending on the polarity of thevoltage applied across it. A piezoresistive (PR) material is pressuresensitive, in that it may have a high or low resistance depending on itscompression. One material of particular interest as a piezo resistivematerial is Samarium Selenium (SmSe). It has been determined that oneinherent difficulty in working with samarium selenium (SmSe) is etchingthe material selectively to aluminum containing contacts. Furtherdetails of the methods of the present disclosure are now discussed withgreater detail with reference to FIGS. 1-5.

FIG. 1 is a flow chart illustrating one embodiment of a subtractiveforming method that includes an etch step for etching samarium andselenium containing layers without removing aluminum containing layers.Beginning at step 1, the method may include providing a material stackincluding a samarium and selenium containing layer 20 and an aluminumcontaining layer 25 in direct contact with the samarium and seleniumcontaining layer 20.

FIG. 2 depicts one embodiment of a partial material stack for forming adevice including a piezoelectric material layer composed of a samariumand selenium containing layer 20. The partial material stack that isdepicted in FIG. 2 includes a supporting substrate 6; an electricallyconductive material layer 10 to provide an electrode that is present onthe supporting substrate 6, and a dielectric layer 15 that is presentatop the electrically conductive material layer 10 that provides theelectrode.

The supporting substrate 6 may be a bulk-semiconductor substrate. In oneexample, the bulk-semiconductor substrate may be a silicon-containingmaterial. Illustrative examples of Si-containing materials suitable forthe bulk-semiconductor substrate that provides the supporting substrate6 include, but are not limited to, Si, SiGe, SiGeC, SiC, polysilicon,i.e., polySi, epitaxial silicon, i.e., epi-Si, amorphous Si, i.e., α:Si,and multi-layers thereof. Alternative semiconductor materials can alsobe employed for the supporting substrate 6, such as, but not limited to,germanium, gallium arsenide, gallium nitride, silicon germanium, cadmiumtelluride and zinc sellenide, as well as other type IV and III-Vsemiconductors. Although not depicted in FIG. 2, the supportingsubstrate 6 may also be a semiconductor on insulator (SOI) substrate oran extremely thin semiconductor on insulator (ETSOI) substrate. Theelectrically conductive material layer 10 is formed atop the supportingsubstrate 6. “Electrically conductive” as used through the presentdisclosure means a material typically having a room temperatureconductivity of greater than 10⁻⁸ (Ω-m)⁻¹. The electrically conductivematerial layer 10 may be composed of a metal or metal nitride. In someembodiments, the electrically conductive material layer 10 is a metalselected from aluminum, copper, tungsten, tantalum, titanium, platinum,tungsten, ruthenium, rhenium, gold, silver, rhodium, molybdenum andcombinations thereof.

In some other embodiments, the electrically conductive material layer 10is comprised of titanium nitride, tantalum nitride, tungsten nitride andcombinations thereof. The electrically conductive material layer 10 maybe formed using a physical vapor deposition (PVD) process, plating,electroplating, and/or electroless plating. In other embodiments, theelectrically conductive material layer 10 may be formed using chemicalvapor deposition (CVD) or atomic layer deposition (ALD). Theelectrically conductive material layer 10 may provide at least oneelectrode for providing electrical communication to the device.

The dielectric layer 15 may be formed top the electrically conductivematerial layer 10 may be any dielectric layer, such as an oxide, e.g.,silicon oxide, nitride, e.g., silicon nitride, or oxynitride, e.g.,silicon oxynitride. Alternatively, high-k dielectrics, such as oxides ofTa, Zr, Al, Hf (e.g., hafnium oxide) or combinations thereof may be usedfor the dielectric layer 15. In another embodiment, the dielectric layer15 is composed of ZrO₂, Ta₂O₅ or Al₂O₃. In one embodiment, thedielectric layer 15 has a thickness ranging from 1 nm to 10 nm. Thedielectric layer 15 may be formed using chemical vapor deposition (CVD),such as plasma enhanced chemical vapor deposition (PECVD).

FIG. 3 depicts patterning a dielectric layer 15 of the partial materialstack for forming the device including the piezoelectric material layer20 to expose a portion of an electrically conductive material layer 10that provides an electrode of the device, and forming a stack of apiezoelectric material layer 20 of samarium and selenium and an aluminumcontaining layer 25. The dielectric layer 15 may be patterned usingdeposition, photolithography and etch processes. For example, a patternis produced by applying a photoresist to the surface to be etched;exposing the photoresist to a pattern of radiation; and then developingthe pattern into the photoresist utilizing a resist developer. Once thepatterning of the photoresist is completed, the sections covered by thephotoresist are protected while the exposed regions are removed using aselective etching process that removes the unprotected regions, i.e.,unprotected portion of the dielectric layer 15. The exposed portion,i.e., unprotected portion, of the dielectric layer 15 may then be etchedusing a selective etch process. As used herein, the term “selective” inreference to a material removal process denotes that the rate ofmaterial removal for a first material is greater than the rate ofremoval for at least another material of the structure to which thematerial removal process is being applied. For example, in oneembodiment, a selective etch may include an etch chemistry that removesa first material selectively to a second material by a ratio of 100:1 orgreater. In one example, the exposed portion, i.e., unprotected portion,of the dielectric layer 15 is removed selectively to the underlyingelectrically conductive material layer 10. The exposed portion, i.e.,unprotected portion, of the dielectric layer 15 gate structure 30 may beremoved using a wet or dry etch process. In one embodiment, the exposedportion, i.e., unprotected portion, of the dielectric layer 15 isremoved by reactive ion etch (RIE). The portion of the dielectric layer15 removed to expose the underlying electrically conductive materiallayer 10 may be referred to as a window.

The piezoelectric material layer 20 of samarium and selenium may bedeposited overlying the remaining portion of the dielectric layer 15 andin direct contact with the electrically conductive material layer 10through the window that is formed in the dielectric layer 15. Thepiezoelectric material layer 20 may be formed using chemical vapordeposition (CVD), physical vapor deposition (PVD), and/or atomic layerdeposition (ALD). Chemical vapor deposition (CVD) is a depositionprocess in which a deposited species is formed as a result of chemicalreaction between gaseous reactants at greater than room temperature (25°C. to 900° C.); wherein solid product of the reaction is deposited onthe surface on which a film, coating, or layer of the solid product isto be formed. Variations of CVD processes include, but not limited to,Atmospheric Pressure CVD (APCVD), Low Pressure CVD (LPCVD) and PlasmaEnhanced CVD (PECVD), Metal-Organic CVD (MOCVD) and combinations thereofmay also be employed. PVD deposition methods may include plating,electroless plating, electroplating, sputtering and combinationsthereof.

The piezoelectric material layer 20 of samarium and selenium may be asamarium and selenium containing layer comprises 10 at. % to 90 at. %samarium (Sm) and 90 at. % to 10 at. % selenium (Se). In someembodiments, the piezoelectric material layer 20 of samarium andselenium may be samarium selenium (SmSe). The samarium selenium (SmSe)layer may comprise 10 at. % to 90 at. % samarium (Sm) and 90 at. % to 10at. % selenium (Se), and can be free of other elements with theexception of impurities. For example, a suitable impurity level may be 1at. % or less. In another example, the impurity level may be 0.5 at. %or less. In yet another example, the impurity level may be 0.1 wt. % orless. In yet another example, the piezoelectric material layer 20 ofsamarium and selenium may be 100 at. % samarium selenium (SmSe). In someother embodiments, the piezoelectric material layer 20 of samarium andselenium may be alloyed with aluminum (Al), chromium (Cr), titanium(Ti), and silicon (Si), and combinations thereof.

The aluminum containing layer 25 is formed directly on the piezoelectricmaterial layer 20 of samarium and selenium. The aluminum containinglayer 25 may be deposited using chemical vapor deposition (CVD), atomiclayer deposition (ALD), physical vapor deposition (PVD) or a combinationthereof. For example, the aluminum containing layer 25 may be depositedusing plating, such as electroplating or electroless plating, as well assputtering. Plating is a method of depositing a layer of metal on adeposition surface. Electroplating is a process that uses electricalcurrent to control the flow of charged particles, such as metal cationsand anions, so that they form a coherent metal coating the depositionsurface. Sputtering is another example of a PVD process that can formthe aluminum containing layer 25.

In one embodiment, the aluminum including material for the aluminumcontaining layer 25 is a pure aluminum, i.e., 100 at. % aluminum. Thepure aluminum may include incidental oxidation of the aluminum. Inanother embodiment, the aluminum including material is a mixture ofaluminum and one or more other metals. An aluminum-metal mixture can bea heterogeneous mixture, or alternatively, a homogeneous mixture, suchas an alloy. Generally, the alloys considered herein contain aluminum inan amount of at least 40% by weight of the alloy, and more generally, atleast 50%, 60%, 70%, 80%, 90%, 95%, 97%, 98%, or 99% by weight of thealloy. In some embodiments, the aluminum containing layer 25 may bealloyed with chromium (Cr), titanium (Ti), and silicon (Si), andcombinations thereof.

It is noted that any composition including aluminum may be employed forthe aluminum including layer 25, so long as the composition iselectrically conductive.

FIG. 4 depicts one embodiment of patterning the aluminum containinglayer 25. Referring to Step 2 of FIG. 1, patterning the aluminumcontaining layer 25 may begin with forming a photoresist mask 30, asdepicted in FIG. 4. For example, a photoresist mask 30 can be producedby applying a photoresist to the surface to be etched; exposing thephotoresist to a pattern of radiation; and then developing the patterninto the photoresist utilizing a resist developer to provide thephotoresist mask 30, wherein the sections of the aluminum containinglayer 25 covered by the photoresist mask 30 are protected, while theexposed regions are removed in a following etch process.

Referring to step 3 of the process flow illustrated in FIG. 1, in afollowing process step, the aluminum containing layer 25 may bepatterned, i.e., etched, as depicted in FIG. 4. The etch process forremoving the exposed portions of the aluminum containing layer 25 can beselective to at least one of the photoresist mask and the underlyingpiezoelectric material layer 20 of samarium and selenium. The etchprocess may be a dry etch process or a wet chemical etch process. Theetch process may be anisotropic. Examples of anisotropic etch processesthat are suitable for this stage of the present disclosure includereactive ion etch (RIE), laser etching, laser milling, gas plasmaetching and combinations thereof.

Step 4 of the process flow illustrated in FIG. 1 can include etching thesamarium component of the samarium and selenium containing layer 20 ofthe exposed portion of the material stack with an etch chemistrycomprising citric acid and hydrogen peroxide that is selective to thealuminum containing layer 25.

FIG. 5 depicts one embodiment of etching the samarium component of thesamarium and selenium containing layer of the exposed portion of thematerial stack with an etch chemistry comprising citric acid andhydrogen peroxide that is selective to the aluminum containing layerfollowed by a high temperature process.

In some embodiments, during etching the samarium component of thesamarium and selenium containing layer 20 with the etch chemistry ofcitric acid and hydrogen peroxide that is selective to the aluminumcontaining layer, the hydrogen peroxide reacts with the aluminumcontaining layer to provide an oxide etch protectant surface on thealuminum containing layer. For example, the oxide etch protectantsurface may be composed of aluminum oxide (Al₂O₃).

In some embodiments, during etching the samarium component of thesamarium and selenium containing layer 20 with the etch chemistry ofcitric acid and hydrogen peroxide that is selective to the aluminumcontaining layer, the citric acid etches samarium selectively to theoxide etch protectant surface that is present on the aluminum containinglayer.

The etch chemistry is typically a wet etch. In some embodiments, theetch chemistry comprises hydrogen peroxide in an aqueous solution in anamount ranging from 1 wt/wt % to 20 wt/wt %, with citric acid present inthe aqueous solution in an amount ranging from 1 wt/wt % to 20 wt/wt %.It is noted that the aforementioned composition is only one example of aetch composition for removing the samarium component of the samarium andselenium containing layer that provides the piezoelectric material layer20.

In some examples, the aqueous etch solution that is suitable for etchingthe samarium component may include citric acid in combination withhydrogen peroxide, in which the portion of citric acid is equal to 1wt/wt %, 2 wt/wt %, 4 wt/wt. %, 6 wt/wt %, 8 wt/wt %, 10 wt/wt %, 12wt/wt %, 14 wt/wt. %, 16 wt/wt %, 18 wt/wt %, 20 wt/wt % and 25 wt/wt %,or any range including one of the aforementioned values as the lowerendpoint of the range, and one of the aforementioned values as the upperendpoint of the range. In some examples, the aqueous etch solution thatis suitable for etching the samarium component may include citric acidin combination with hydrogen peroxide, in which the portion of hydrogenperoxide is equal to 1 wt/wt %, 2 wt/wt %, 4 wt/wt. %, 6 wt/wt %, 8wt/wt %, 10 wt/wt %, 12 wt/wt %, 14 wt/wt. %, 16 wt/wt %, 18 wt/wt %, 20wt/wt % and 25 wt/wt %, or any range including one of the aforementionedvalues as the lower endpoint of the range, and one of the aforementionedvalues as the upper endpoint of the range.

In some embodiments, the etching of the samarium component of thesamarium and selenium containing layer of the exposed portion of thematerial stack with the etch chemistry comprising citric acid andhydrogen peroxide comprises applying the etch chemistry to the materialstack at room temperature, e.g., 20° C. to 25° C. In some otherembodiments, the temperature of the etch process may be slightlyelevated from room temperature.

In some embodiments, the etching of the samarium component of thesamarium and selenium containing layer 20 of the exposed portion of thematerial stack with the etch chemistry comprising citric acid andhydrogen peroxide includes a time period ranging from 5 seconds to 10minutes. In another embodiment, the time period for this etch stage mayrange from 15 seconds to 5 minutes. In other examples, the time periodfor the application of the citric acid and hydrogen peroxide wet etch isequal to 15 seconds, 30 seconds, 45 seconds 1 minute, 2 minutes, 3minutes, 4 minutes and 5 minutes, as well as any range of time includinga lower limit selected from the aforementioned examples, and an upperlimit selected from the aforementioned examples.

The method may continue at step 5 of the process flow illustrated inFIG. 1 with removing a remaining selenium component of the samarium andselenium containing layer 20 by elevating a temperature of the seleniumcomponent above a heat of vaporization for the selenium component. Theremaining selenium component is vaporized by the increased heat. Theremaining component of the piezoelectric layer 20 that is vaporized byheating may include selenium (Se), sulfur (S), and tellurium (Te) andcombinations thereof. Elevating the temperature of the etched surfacetypically occurs after the wet etchant for removing the samariumcomponent of the samarium and selenium containing layer 20 has beenremoved.

In some embodiments, removing the remaining selenium component of thesamarium and selenium containing layer 20 includes heating in a furnaceat a temperature greater than 100° C. for a time period greater than 1minute, e.g., 5 minutes or greater. In some embodiments, the temperaturefor vaporizing the remaining selenium component of the samarium andselenium containing layer 20 may range from 100° C. to 600° C. In someexamples, the temperature for removing the remaining selenium componentof the etched samarium and selenium containing layer 20 may be equal to150° C., 200° C., 250° C., 300° C., 350° C., 400° C., 450° C., 500° C.,550° C. and 600° C., as well as any range of temperatures including alower limit provided by one of the aforementioned examples and an upperlimit provided by one of the aforementioned examples. In some examples,the time period for the removing the remaining selenium component of thesamarium and selenium containing layer 20 may be equal to 1 minute, 5minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, 30 minutes, 35minutes, 40 minutes, 45 minutes, 50 minutes, 55 minutes and 60 minutes,as well as any range of time including a lower limit provided by one ofthe aforementioned examples and an upper limit provided by one of theaforementioned examples. The temperature for vaporizing the remainingselenium component of the samarium and selenium containing layer 20 maybe raised by furnace anneal, rapid thermal anneal (RTA), laser anneal,electromagnetic annealing, forced air heat, and combinations thereof. Insome embodiments, heating the material stack comprises a nitrogencontaining atmosphere.

Methods as described herein may be used in the fabrication ofpiezoelectric devices that can be used with integrated circuit chips.The resulting integrated circuit chips can be distributed by thefabricator in raw wafer form (that is, as a single wafer that hasmultiple unpackaged chips), as a bare die, or in a packaged form. In thelatter case the chip is mounted in a single chip package (such as aplastic carrier, with leads that are affixed to a motherboard or otherhigher level carrier) or in a multichip package (such as a ceramiccarrier that has either or both surface interconnections or buriedinterconnections). In any case the chip is then integrated with otherchips, discrete circuit elements, and/or other signal processing devicesas part of either (a) an intermediate product, such as a motherboard, or(b) an end product. The end product can be any product that includesintegrated circuit chips, ranging from toys and other low-endapplications to advanced computer products having a display, a keyboardor other input device, and a central processor.

While the present disclosure has been particularly shown and describedwith respect to preferred embodiments thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formsand details may be made without departing from the spirit and scope ofthe present disclosure. It is therefore intended that the presentdisclosure not be limited to the exact forms and details described andillustrated, but fall within the scope of the appended claims.

What is claimed is:
 1. A subtractive forming method comprising: for amaterial stack including a samarium and selenium containing layer and analuminum containing layer in direct contact with the samarium andselenium containing layer: etching the samarium component of thesamarium and selenium containing layer of the exposed portion of thematerial stack with an etch chemistry comprising citric acid andhydrogen peroxide that is selective to the aluminum containing layer;and removing a remaining selenium component of the samarium and seleniumcontaining layer in the exposed portion of the material stack byelevating a temperature of the selenium component above a heat ofvaporization for the selenium component.
 2. The method of claim 1,wherein the samarium and selenium containing layer comprises 10 at. % to90 at. % samarium (Sm), and 90 at. % to 10 at. % selenium (Se).
 3. Themethod of claim 1, wherein the aluminum containing layer comprisesgreater than 95 at. % aluminum (Al).
 4. The method of claim 1, furthercomprising masking the material stack to expose a portion of thematerial stack to be etched, masking including forming a photoresistmask.
 5. The method of claim 1, wherein the etch chemistry compriseshydrogen peroxide in an aqueous solution in an amount ranging from 1wt/wt % to 20 wt/wt %, with citric acid present in the aqueous solutionin an amount ranging from 1 wt/wt % to 20 wt/wt %.
 6. The method ofclaim 1, wherein etching the samarium component of the samarium andselenium containing layer of the exposed portion of the material stackwith the etch chemistry comprising citric acid and hydrogen peroxidecomprises applying the etch chemistry to the material stack at roomtemperature.
 7. The method of claim 1, wherein said etching the samariumcomponent of the samarium and selenium containing layer of the exposedportion of the material stack with an etch chemistry comprising citricacid and hydrogen peroxide comprises a time period ranging from 15seconds to 5 minutes.
 8. The method of claim 1, wherein said removingthe remaining selenium component of the samarium and selenium containinglayer in the exposed portion of the material stack by elevating thetemperature of the selenium component comprises heating the materialstack following said etching in a furnace at a temperature greater than100° C. for a time period greater than 5 minutes.
 9. The method of claim8, wherein said heating the material stack comprises a nitrogencontaining atmosphere.
 10. A subtractive forming method comprising:etching a samarium component of a samarium and selenium containing layerof a material stack with an etch chemistry that is selective to analuminum containing layer in direct contact with the samarium andselenium containing layer; and removing a remaining selenium componentof the samarium and selenium containing layer of the material stack byelevating a temperature of the selenium component above a heat ofvaporization for the selenium component.
 11. The method of claim 10,wherein the samarium and selenium containing layer comprises 10 at. % to90 at. % samarium (Sm), and 90 at. % to 10 at. % selenium (Se).
 12. Themethod of claim 10, wherein the aluminum containing layer comprisesgreater than 95 at. % aluminum (Al).
 13. The method of claim 10, furthercomprising masking the material stack to expose a portion of thematerial stack to be etched, masking including forming a photoresistmask.
 14. The method of claim 10, wherein the etch chemistry compriseshydrogen peroxide in an aqueous solution in an amount ranging from 1wt/wt % to 20 wt/wt %, with citric acid present in the aqueous solutionin an amount ranging from 1 wt/wt % to 20 wt/wt %.
 15. The method ofclaim 10, wherein the etch chemistry includes citric acid and hydrogenperoxide; and wherein etching the samarium component of the samarium andselenium containing layer of the material stack comprises applying theetch chemistry to the material stack at room temperature.
 16. The methodof claim 10, wherein the etch chemistry includes citric acid andhydrogen peroxide; and wherein etching the samarium component of thesamarium and selenium containing layer of the material stack comprisesapplying the etch chemistry for a time period ranging from 15 seconds to5 minutes.
 17. The method of claim 10, wherein said removing theremaining selenium component of the samarium and selenium containinglayer of the material stack by elevating the temperature of the seleniumcomponent comprises heating the material stack following said etching ina furnace at a temperature greater than 100° C. for a time periodgreater than 5 minutes.
 18. The method of claim 17, wherein said heatingthe material stack comprises a nitrogen containing atmosphere.